Light source for use in the photographic recording of sound



" March 7,1939 0 K KOLB 2,149,967

LIGHT SOURCHFOR USE IN 'ILHE PHOTOGRAPHIC RECORDING OF SOUND Filed Aug. 5, 1936 Orra Kym (01.5

Patented Mar. 7, 1939 UNITED STATES LIGHT SOURCE FOR USE IN THE- PHOTO- GRAPHIC RECORDING OF SOUND.

Otto Kurt Kolb, Chiswick, London,.England, as-

signor to British Acoustic Films Ltd., London,

England Application August 3, 1936, Serial No. 94,013 In Great Britain August 23, 1935 1 Claim.

The present invention relates to systems for photographicallyrecording sound on films and like continuous records utilizing high intensity light sources.

It has been customary in the art to use various electrical light sources, particularly of the incandescent lamp type and discharge tubes of mercury vapor and other type, which have projected beams of light through various known types of electro-optical and phono-optical recording systems on to negative or master record films.

It is very desirable to use light sources of high intensity particularly for the recording of sound at high speed and with high frequency components and for recording on relatively insensitive media.

Discharge lamps have been proposed for general lighting purposes of a kind which contain a metallic vapor, which may be that of mercury and which under working conditions is at very high pressure, for example, of or above 100 atmospheres. The container of the lamp employed is preferably formed of quartz or like infusible material, provided with sealed-in electrodes of a metal of high melting point, such as tungsten. In order both to restrict the discharge and to present a small area of container to the very high presssures involved, the discharge tube of such lamps is formed of capillary dimensions or of very restricted bore, and the parts adjacent to the electrodes may be provided with cooling arrangements. Together with a metal vapor as above referred to, the lamp may contain a portion of one or more of the noble or rare gases, such as argon, neon or helium.

The present invention relates to the application of such extremely high intensity light sources to the recording of sound on film. According to a feature of the invention, lamps of the kind referred to are fed from alternating or continuous current sources. In the case of alternating current, this is of supersonsic frequency, the current being constant in amplitude and periodicity when records of the variable area type are to be recorded.

For the production of records of the variable density type, the supersonic alternating or oscillatory current may be modulated by the impressed phonic current to be recorded. It is preferred, however, in this case also, that the supersonic current be maintained steady in frequency and amplitude and the emitted light be modulated by an electro-optical light valve. Supersonic current can, for the purpose of feeding the lamp, be produced by any of the known electrical systems, from current of continuous or low frequency alternating character.

According to the invention, high intensity light sources of the kind referred to are preferably formed as rectilinear tubes of diameters small as 5 compared with their lengths, and having suitable terminal portions into which leading-in conductors are fused. The central linear portion comprising the discharge path of such a tube may be defined at its ends by suitable masks, through which the tube may pass, and such masks may serve also as heat radiating fins.

For the more explicit definition or illustration of typical recording arrangements, utilizing high intensity light sources, reference will be made to Figs. 1 to 3 of the appended drawing.

In one arrangement, first to be described, a linear image of the narrow rectilinear luminous discharge path may be formed by a suitable optical system at a focal plane whereat an opaque shutter is adapted to vibrate transversely to the light beam and to the linear image. The opaque shutter has a serrated or toothed boundary or aperture, the inclined edges ofwhich intercept the light beam and cutoff-varying lengths of the image, as it vibrates.

The light passing the shutter is focused upon the surface of the recording film by a secondary optical system and impresses on said film images of the parts of the first real image of the light source not intercepted by the vibrating shutter. A cylindrical lens may be interposed in the secondary optical system, in order to render the partial images extremely narrow. Such an optical system requires no mechanical slit. The partial collinear images lie in this arrangement transversely to the line or motion of the recording film. The vibratory opaque shutter may be very conveniently oscillated by attachment to a pair of wires carrying phonic current and stretched in a magnetic field directed transversely to the length of the suspending wires and to the plane of shutter vibration.

An arrangement of this kind is illustrated, as an example, in Fig. 1 of the drawing. In this: figure, a source of high frequency current a is connected to the discharge tube b which comprises the straight capillary portion bl and the slightly enlarged terminal chambers b2 and b3 into which suitable discharge electrodes b4 and D5 are sealed.

These latter portions are preferably masked by the screens cl and 02 which may be used if desired as heat radiating fins. The light from the linear portion of the tube is focused by means of the opticalsystem on to the indented or serrated edge of the shutter s and in its plane, pro-v duces an image of the line source. The shutter s'is mounted on the elastic wires or ribbons sl and s2 which carry the required phonic and/ or control currents. These wires lie in a magnetic field maintained between the pole pieces pl and p2, which at the points where they would obscure the light beam proceeding to the shutter,-are each cut away in a cleft or aperture as'at p3'and p4.

' The portions of the light beam not intercepted at any moment by the vibrating shutter s are by means of the optical system 02 caused to form separate variable lengths collinear line images as at rl, r2, r3 on the surface of theifllm ,f and thereon produce a series of tracks each of the double-hump type. r

In a modification of the apparatus, anoscillograph mirror may receive a light beam from the high intensity light source arranged as previously set'forth and an optical system may form an image thereof delimited by'means of a mask provided-with a screening edge on the film surface. The image may be vibrated in its own length transversely to the line of motion of a record film.

A system of this kind is indicated schematically in Fig. 2 of the drawing. Herein, the straight and capillary portion bl of the light source is projected by means of a condensing lens or lens system 03 onto the oscillograph mirror m and is therefrom reflected; and by the aid'of the cylindrical lens 04 forms an exceedingly brilliant image of the light source which is reduced to a line of restricted width on the film. A screenor "diaphragm d provided with a slot dl is disposed I defining edge d4 lying transverse to the length of the linear image, which is vibrated across this edge, whereby a varying proportion of its length falls upon the travelling film and consequently produces a single hump record thereon.

In a further modified arrangement utilizing a high intensity source, the elongated image of the light source is formed of sufficient width to cover a light valve constituted by two oppositely vibrating wires or ribbons disposed in a transverse magnetic field. Such an arrangement acts as a light valve quantitatively varying the light flux passing between the ribbons and by the use of a suitable opticalsystem a. linear image of varying intensity for the constant width may be produced by said light flux upon the record film, producing a a record of variable density type on its surface. Apparatus so arranged is schematically shown in Fig; 3 of the drawing. In this figure, light passing from the capillary discharge tube bl is focused by means of the optical system ol, which in this case may comprise a cylindrical lens 01 on to the light valve 1, the active part of which is constituted l2 disposed in a mag-v by the two ribbons I l, netic field transverse to the plane in which they vibrate. Light passing between the two ribbons is focused by the optical system 06 on the' surface of the film ,f, producing a variable density record thereon.

Apparatus utilizing the invention may be constructed in various specifically referred to herein; by thoseversed in the art, without departing from its 'scope and nature as defined in the appended claim.

What I claim is:

In a system for photographically recording sound on film, a source of light comprising a discharge lamp containing a metallic vapor at very high pressure, an electro-optical system for producing upon the film a linear image of light from said source, means including an oscillograph for longitudinally vibrating said image under the influence of phonic; currents and for vibrating said image transversely to the line of motion of the film, whereby a single hump sound record will be produced on the latter.

oTro KURT KOLB.

forms other than those 

